1.Keane bought some marbles and gave half of them to Leon. Leon
bought some stamps and have half of them to Keane.

Keane used 5 stamps and Leon gave away 11 marbles. The ratio of
the number of stamps to the number of marbles Keane had left then
became 1:7 and the ratio of the number of stamps to the number of marbles Leon had left became 1:5

1.Keane bought some marbles and gave half of them to Leon. Leon
bought some stamps and have half of them to Keane.

Keane used 5 stamps and Leon gave away 11 marbles. The ratio of
the number of stamps to the number of marbles Keane had left then
became 1:7 and the ratio of the number of stamps to the number of marbles Leon had left became 1:5

How many stamps did Leon buy?

Thanks.

Is this a PSLE 5 yr series question? Thought it look familiar.

Here's the solution:

Use units and parts.

Keane----S:M = 1u:7u
Leon----S:M = 1p:5p

Since Keane bought only marbles and he gave half to Leon, this implies that
7u = 5p +11---(1)

Since Leon bought only stamps and gave half to Keane, this means that
1p = 1u + 5 ---(2)